GB2084705A - Blast furnace casting system and method of suppressing theformation of pollutants in such a system - Google Patents

Description

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GB 2 084 705 A 1

SPECIFICATION

Blast furnace casting system and method of suppressing the formation of pollutants in such a 5 system

The present invention concerns a blast furnace casting system and a method of suppressing the formation of pollutants in such a blast furnace 10 casting system.

The invention relates more particularly to the control of fume formation in steel mill blastfurnace cast houses and to the suppression and mitigation of

* fumes from the iron troughs and the iron and the 15 slag runners of the blastfurnace casting system.

One of the most critical problems faced by the

* steel industry is the control of blastfurnace cast house emissions. It is evident that the industry must develop new techniques for pollution controls if it is

20 to obviate the substantial capital and operating costs associated with available technology for controlling blast furnace cast house emissions to levels required by governmental environmental protection agencies. Technology for emission reduction through gas 25 cleaning exists and can be accomplished by a number of air pollution control devices which utilize exhaust and filtering equipment which collect and clean the fugitive air. However, it should be recognized that in the United States a great majority of the 30 presently operating blastfurnaces were built before 1960 and use the original cast houses in which there are spatial limitations toward retrofitting additional equipment such as pollution collection devices.

The known prior art fume control systems which 35 can be used in conjunction with steel mill blast furnaces are directed to the disposal of the fume after it has been generated.

U.S. Patent 3 994 210 discloses a method and apparatus by which jets in the form of moving 40 curtains of air are utilized to control and direct the movement of fume from a fume-generating apparatus to an exhaust hood opening.

French Patent 71 13332 is more specifically directed to the channeling of smoke emitted by 45 molten cast iron as it is extracted from a blast furnace through the use of blower nozzles which laterally direct air curtains to limit lateral movement of the smoke and direct it to a ventilating head.

German Patent 2 157 418 discloses an air cleaning 50 device for the pouring platform of a blastfurnace, which device comprises suction nozzles connected to a gas cleaner at the outlets of the filling hoppers and/or over the tap holes.

Additionally, there appears in the August 1979 55 issue of Iron and Steel Engineer, pp. 33-39, an article entitled "Blast Furnace Cast House Emission Control" by A.G. Nicola which sets forth the available technology for collecting the process fugitive emissions generated in the blast furnace cast house. 60 It is evident that most prior art fume pollution control systems are addressed to the ventilation or exhausting of fumes after they are formed, i.e., they are addressed to the effect rather than the cause.

It is a primary object of this invention to provide 65 method and apparatus to suppress and/or mitigate the formation of objectionable fume dring the tapping of a blast furnace and the flow and pouring of iron therefrom.

In blast furnace case houses much fume is generated during the tapping of the furnace. It is believed that most of the fume is generated by the iron leaving the furnace contacting the oxygen of the ambient air and thereby forming iron oxide. Some of the fume is also generated by virtue of the sulfur in the molten iron and/or slag coming into contact with oxygen and forming sulfur dioxide.

This invention proposes to suppress the formation of obnoxious fume by providing method and apparatus for isolating much of the air from the molten metal and slag streams as they are discharged from the blastfurnace and/or from the molten streams as they flow toward and to the collection vessels.

In the aforementioned Nicola article it is pointed out that basically, the fumes generated in the case house are approximately 75% iron oxide and there is also outlined the reasons why the transfer of Japanese technology for cast house emission control on existing blastfurnaces in the United States is not a simple matter. It further discloses that the primary emission control based upon the Japanese approach consists of capturing the cast house fumes at their source with close fitting hoods. It is very apparent that while hoods and other enclosures are described as being part of the Japanese approach such enclosures are employed as ductwork for directing the ventilating air with the entrained pollutants to collection devices such as baghouses.

Thus, the Nicola article points up the fact that prior cast house emission control is primarily concerned with the evacuation of fumes and emissions after they are formed. The present invention is contradis-tinctive because it is concerned with the suppression of the formation of the iron oxide fumes. The invention provides method and apparatus which exclude oxidizing gases, including the ambient air, during the tapping of the blastfurnace from the area surrounding the tap hole, the iron trough and the iron and the slag runners, it will be recognized that it may not be possible to provide an absolutely air tight system, however, the formation of iron oxide and other pollutants formed by combining with oxygen is suppressed, primarily because there is no purposeful addition of air as an evacuation medium as there is in ventilating systems. However, it will be understood that an inert gas may be circulated over the molten streams from the blast furnace to occlude oxidizing gases and more particulaly to restrain the infiltration of ambient air into the molten streams.

In order that the invention may be fully understood references is made on the following drawings, wherein :

Figure 7 is a schematic representation in plan view of atypical blastfurnace and runner system;

Figure 2 is a side elevation view of fragmentary portion of a blastfurnace and an iron trough together with an enclosure of this invention for the iron trough;

Figure 3 is a cross-sectional view taken along line 3-3 of Figure 2;

Figure 4 is a transverse cross-sectional view of an

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enclosure for the iron and the slag runners; and

Figure 5 is a fragmentary longitudinal sectional view of two adjacent enclosures of the type shown in Figure 4 shown in conjunction with a runner gate 5 and means for creating end curtains.

Atypical embodiment of this invention is illustrated in Figure 2 in conjunction with a blastfurnace cast house system such as schematically illustrated in Figure 1. It will be appreciated by those skilled in 10 the art that there are many variations of the iron trough, iron runners, and slag runners used in connection with a blast furnace with which the principals of this invention can be applied.

The blast furnace and the discharge notch are 15 generally designated by the reference characters BF and N, respectively. The molten material, comprising iron and slag, is tapped from the furnace BF through the notch N which extends downwardly from the outside of the furnace through the water 20 cooled hearth jacket toward the hearth. The notch N is plugged after each cast with a clay mixture forced in the notch hole under pressure by means of a mud gun (not shown) which is latched onto latch support LS. As the notch N is opened during a tapping, the 25 molten material flows out into a large trough IT, generally referred to as an iron trough. There is skimmer means S at the end of the trough IT which werves to skim off the slag from the molten material in the trough. The skimmer means S in some 30 systems may include a dam (not shown) which may serve to help maintain the level of the molten material higherthan the bottom of the skimmer plate. At the skimmer S there is an arrangement of gates G and runners SR to carry off the slag S to slag 35 collector means SC, such as a slag pot or a large pit. The iron flowing under the skimmer plate runs down troughs !R, commonly referred to as iron runners, which are also fitted with gates G to selectively divert the flow to each of several iron ladles IL. At the 40 end of a cast or tapping, the mud gun is placed in position to plug the notch hole with clay. It is at this stage that special provision must be made to handle the section of enclosure surrounding the tap or notch hole in order to provide access by the mud 45 gun to the notch.

As indicated above, the present invention relates to the provision of method and apparatus for occluding the ambient airfrom the surface of the molten stream as it flows from the blastfurnace 50 toward the iron ladle and the slag collection means. In accordance with a preferred embodiment of the invention occlusion means in the form of hoods H are provided to minimize the amount of ambient air which contacts the molten streams and without the 55 addition of any air within the hoods as is the practice in ventilating hoods. The various types of hoods are further designated by numeral suffixes.

There is provided immediately adjacent to the blast furnace BF a hood H-1 which covers the iron 60 trough. It is preferred to provide separate hoisting and transport mechanism, generally designated by the reference HTM, for lifting and movng the hood H-1 away from the tap hole in preparation for the tapping and plugging procedures. The cross-65 sectional configuration of hood H-1 is preferably in the form of an inverted U.The hood H-1 is comprised of several panel sections P which are joined together, such as by welding the upturned edges of the outer casings which form stiffering flanges. The 70 section P-1 has a slanted top tapered toward the blastfurnace and terminating in a nose portion to provide an end closure which will also accomodate positioning of the hood H-1 beneath the clay gun support LS. The opposite end section P-2 has a 75 vertical wall portion W-1 to likewise provide an end closure. Each of the sections P are provided with insulation to protect the metal cover. Preferably,

there are provided two layers of insulation anchored to the cover by metal clips, the innermost layer L-1 in 80 respect to the trough, being ofthe non-consumable refractory type and the outermost layer L-2, in respect to the trough, having higher insulating quality than the layer L-1. Each ofthe layers L-1 and L-2 may be applied as by gunning, at the site. 85 Some ofthe sections, such as section P-3, are provided with upstanding flanges F which define holes for inserting the fastening means such as hooks ofthe hoising and transport mechanism HTM. The hoods H-2 are provided to enclose the iron 90 runners IR and the slag runners SR. The hoods H-2 are similar in construction as hood H-1 except that they are smaller in their cross-sectional configurations. Also, in a preferred form, the hoods H-2 include the end vertical wall closures W-2. This end 95 wall W-2 may be supplemented with a flexible blanket of insulating material B draped over support rod R or a curtain of inert gas through conduit means such as pipe C-1. Preferably, pipe C-1 is formed to correspond to the end cross-section of hood H-2, i.e., 100 it is generally semi-circular in shape and has a plurality of nozzles for discharging the inert gas and creating the vertical curtain or blanket for occluding the ambient air. The pipe is suitably attached to line supply means through releasable coupling means. 105 The reason for preferring the inert gas curtain type of end seal is that the height ofthe molten material in the runners will vary and hence it would be impossible to provide a mechanical seal which would be self-adjusting to compensate for the variations in the 110 height of the material flow.

Alternatively and/or additionally, inert gas supply means may be provided within the hoods H in the form of conduit C-2 which extend longitudinally of and on either or both sides of and within the hoods 115 H. The hoods H would thus serve to contain the inert gases and create a blanket over the surfaces ofthe molten material. In a less preferred embodiment the inert gases would be used to create a blanket in the s absence ofthe confining hoods H through the use of 120 pipe means extending longitudinally of each side of the troughs and runners. 4

Alternatively and/or additionally, an inert non-combustible material such as vermiculite may be provided on top of the iron or slag to create a 125 floating blank FBoverthe surface ofthe molten material MM. This floating blanket would bekeptin position by the use of suitable means, e.g., a suspended carbon skimmer which extends just below the surface ofthe molten material.

130 Also there may be provided between the hoods H

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GB 2 084 705 A 3

and the tops ofthe troughs and runners yieldable non-combustible sealing means SM, such as sand or refractory fiber felt.

Thus, unlike the prior art systems which rely upon 5 evacuating the cast house air with entrapped emissions, the present invention is directed toward restraining the formation ofthe objectionable pollutants. Through the use ofthe method and apparatus of this invention the occlusion ofthe ambient cast 10 house airfrom the surface ofthe molten iron and slag is enhanced and the formation of iron oxides is suppressed. A further advantage ofthe present invention is one of confining the natural kish which I is formed on the surface ofthe molten iron. A still -15 further and important advantage is that the "hot metal", molten iron, is delivered to the iron ladles at # a relatively high temperature since there are no massive air currents moving across the surface of the molten iron in the troughs as there are in 20 ventilating systems. The hotter molten metal and iron runners result in less iron skull formation in the runners and a concomitant increase in iron yield.

Still further, the invention provides method and apparatus which may be readily and safely embo-25 died in existing blastfurnace cast house systems and at relatively little cost as compared to pollutant collection systems, which require additional equipment and space for the ducts and filter baghouses, which collection systems also pose health and safety 30 hazards because ofthe problems encountered in the disposal of the collected dust. A further disadvantage of such collection systems is that they consume considerable energy as compared to the system of this invention.

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Claims (14)

1. A method of suppressing the formation of pollutants in a blastfurnace casting system, char-

40 acterized in that said method comprises restraining contact of oxidizing gases, including the ambient air, with the surface ofthe molten streams discharged from the blast furnace and flowing in at least one of the iron troughs, the iron runners, and the slag 45 runners ofthe casting system.

2. The method according to claim 1, characterized in that contact of ambient air with said surface is restrained by enclosing at least one of said iron troughs, iron runners, and slag runners with hood

50 means and in the absence of any purposefully added oxidizing gases within said hood means.

3. The method according to claim 2, characterized in that an open-hood means is used and a vertical blanket of inert gas is created to restrain

55 entry of ambient air into said open-end hood means.

4. The method according to claim 1, characterized in that said contact is restrained by creating a blanket of inert gases over at least one of said streams.

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5. The method according to claim 4, characterized in that the gases of said blanket are confined by enclosure means.

6. The method according to claim 2, characterized in that a flexible blanket of insulation restrains 65 entry of ambient air into said hood means.

7. A method for suppressing formation of pollutants in a blastfurnace casting system, characterized by the steps of creating a blanket of gases which are non-oxidizing to the molten melt discharged from

70 the blastfurnace over the melt as it flows in at least one ofthe iron troughs, the iron runners, and the slag runners, in the absence of any purposeful addition of any oxidizing gas, including air, to said molten melt and said blanket of gases.

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8. A blastfurnace casting system having molten stream carrier means which includes an iron trough, iron runner, and a slag runner, characterized in that it comprises enclosure means for at least one of said carrier means, which enclosure restrains oxidizing

80 gases, including the ambient air, from contacting the surface ofthe molten stream within said one of said carrier means.

9. The blast furnace casting system according to claim 8, characterized in that said enclosure means

85 comprises a blanket of inert gas.

10. The blast furnace casting system according to claim 8, characterized in that said enclosure means comprises a hood which enhances the occlusion of ambient air and in the absence of a ventilat-

90 ing fluid stream for ventilating said hood.

11. The blastfurnace casting system according to claim 10, characterized in that said enclosure means comprises an open-end hood, and further comprising means for creating a vertical blanket of

95 inert gases at an open-end of said enclosure means for restraining entry of ambient air thereon.

12. The blastfurnace casting system according to claim 8, characterized in further comprising a blanket of natural kish floating on at least a portion

100 of the molten stream.

13. The blastfurnace casting system according to claim 8, characterized in that it further comprises resilient sealing means between said enclosure means and said one of said carrier means.

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14. A blastfurnace casting system having molten stream carrier means which includes an iron through iron runner, and a slag runner, characterized in that it comprises a blanket of insulating material floating on at least a portion ofthe molten stream within said

110 carrier means.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1982.

Published by The Patent Office, 25 Southampton Buildings, London, WC2A1 AY, from which copies may be obtained.